During the second year of this grant work will be directed towards characterizing the leukemic CFUd cell with respect to cell cycle activity and drug sensitivity. We will also direct our efforts towards optimizing the in vitro condition for colony formation by kinetically active and quiescent leukemic cells. The kinetically active and quiescent leukemic cell populations as a whole will be characterized with respect to their sensitivity to the anthracycline antibiotics and to X rays. The effects of purported regulators of DNA synthesis (cyclic nucleotides, etc.) on these cell populations will be studied and we will begin to study enzymatic pathways which are believed to play a role in the regulation of cell proliferation.